Department of Education officials say a fourth error by Pearson in grading city students’ gifted screening exams could be the final straw in their contract with the testing supergiant.

Last month, the department announced that Pearson had made three serious errors when grading the screening tests, leading to nearly 5,000 children getting scores that were lower than they deserved. The department issued new score reports and extended the deadline for applying to gifted programs by three weeks.

Today, on the new application deadline, the department revealed that Pearson had made yet another error. Like the first ones, the mistake was detected only after a parent asked for an explanation of how her child’s score had been calculated, officials said. About 300 additional students’ scores were artificially depressed because of the latest error, according to the department.

Chancellor Dennis Walcott said in a statement that he had lost confidence in Pearson after the company had convinced him that its second attempt to get the scoring right had been thorough and accurate.

“This failure to complete the basic quality assurance checks Pearson confirmed that they had completed is deeply disturbing,” Walcott said. “For this reason, the Department of Education is reviewing a variety of options, including terminating Pearson’s contract.”

After the first errors, Walcott said,  “I have told the company’s officials in no uncertain terms that I expect this will never happen again.”

The city is one year into a $5.5 million contract with the company — which also administers the state’s testing program — to carry out the gifted screening program. Already, the city had docked Pearson $500,000 for the previous errors, announcing plans to use the money to inform families about the errors and bolster schools in neighborhoods where few children qualified for gifted programs.

The latest mistake had to do with accounting for the date on which students took the screening test. In some cases, Pearson’s quality control did not pick up that a default date had been registered, leading to artificially low scores, officials said.

Of the students whose scores were depressed by the test date mistake, 82 students who had not qualified for gifted programs at all are now eligible, and 64 students who had previously qualified only for programs in their district may now apply to elite citywide programs. Another 159 students had their score rise, increasing their chances of admission to gifted programs.

The Department of Education is extending the admission deadline again, to May 17, setting back the citywide “domino effect” that will take place when families that accept the offer in gifted programs withdraw from other schools.

Pearson’s President of Learning Assessment Scott Smith said in a statement, “There’s no excuse for the scoring errors made on the assessments used to determine eligibility for the New York City Gifted and Talented programs. We have already begun to implement the multiple program changes requested by the New York City Department of Education, and Pearson is taking all necessary measures to ensure this doesn’t happen again. We’ve extended our apologies to our colleagues at the NYC DOE, and we’re very sorry to all the families and students who have been affected.”

Meanwhile, since the day that the company first announced its gifted testing mistakes, its stock price has risen, slightly outperforming the market.